Electric axial flow machine

ABSTRACT

An electric axial flow machine includes an ironless disk-shaped rotor arranged on a machine shaft and having permanent magnets embedded in a fiber- or fabric-reinforced plastic, and, on both sides, next to the rotor, a stator, wherein the permanent magnets are each joined to the surrounding fiber- or fabric-reinforced plastic so that the permanent magnets and the machine shaft form a dimensionally stable unit.

The present invention relates to an electric axial flow machines asdefined in the precharacterizing clause of the independent patent claim1.

BACKGROUND

1. Field of the Invention

An electric axial flow machine is understood as meaning a motor orgenerator with a rotor and a stator, in which the magnetic flux betweenthe rotor and the stator is parallel to the axis of rotation of therotor. Axial flow machines of this type are also known by thedesignations brushless DC motor, permanent-magnet synchronous motor ordisk-armature motor.

An efficient brushless DC motor with an ironless rotor arranged around ashaft and having permanent magnets is described for example in DE-U-29816 561. In the case of this DC motor, arranged around the shaft on bothsides of the disk-shaped rotor, and parallel to the rotor, there is ineach case an electromagnet unit as a stator. The rotor has permanentmagnets which are arranged in a circular manner around the shaft, areembedded for example in a plastic and the direction of magnetization ofwhich runs parallel to the shaft. Two neighboring permanent magnetsrespectively have a reversed direction of magnetization. One stator isprovided with first electromagnetic regions and the other stator isprovided with second electromagnetic regions, the number of whichcorresponds to the number of permanent magnets, two neighboring firstelectromagnetic regions and two neighboring second electromagneticregions in each case having reversed directions of magnetization, whichare changed alternately. The first and second electromagnetic regionsare arranged offset in relation to one another and have a phasedifference of 90°.

One disadvantage of this DC motor is that the rotor is, by its nature,relatively unstable and therefore suitable only for slow rotations.

U.S. Pat. No. 5,619,087 discloses an electric axial flow machine whichcomprises at least two ironless disk-shaped rotors with relativelysmall, bar-shaped permanent magnets, which are embedded in a fiber- orfabric-reinforced plastic. A plurality of like-magnetized permanentmagnets arranged next to one another respectively form a group, whichforms one magnetic pole. The fact that many relatively small permanentmagnets are arranged in the plastic instead of a number of large magnetshas the effect of reducing the effective magnetic area, and consequentlythe magnetic flux, which is compensated by the use of at least tworotors. Furthermore, the anchoring of the many individual permanentmagnets in the plastic presents problems in terms of production andstrength.

SUMMARY OF THE INVENTION

In view of the disadvantages of the previously known axial flow motorsand generators, the invention is based on the following object. The aimis to provide an electric axial flow machine, the rotor of which is aslow in mass and inertia as possible, but nevertheless stable and alsosuitable for high rotational speeds.

An important feature of the invention is that, in an electric axial flowmachine with an ironless disk-shaped rotor which is arranged on amachine shaft and has permanent magnets which are embedded in a fiber-or fabric-reinforced plastic, the permanent magnets are each joined witha positive fit to the surrounding fiber- or fabric-reinforced plasticand the latter, together with the permanent magnets and the machineshaft, forms a dimensionally stable unit. Arranged next to the rotor onboth sides there is in each case a stator.

The mere fact that the plastic is fiber- or fabric-reinforced means thatthe rotor has great rigidity. This is further increased by the fact thatthe permanent magnets are each joined with a positive fit to thesurrounding fiber- or fabric-reinforced plastic and the latter, togetherwith the permanent magnets and the machine shaft, forms a dimensionallystable unit. The latter can be achieved by suitable arrangement of thepermanent magnets and the machine shaft and molding of the fiber- orfabric-reinforced plastic. The design of the rotor according to theinvention makes the rigid permanent magnets serve at the same time asstiffening elements, it being ensured by the positive connection withthe surrounding plastic that the permanent magnets do not becomedetached.

A plurality of permanent magnets are advantageously arranged in acircular manner around the machine shaft, and the plastic, in particulara thermosetting material, advantageously extends between the permanentmagnets altogether over at least 10%, preferably between 15% and 20%, ofthe circle. By arranging and embedding the permanent magnets in such away, the rotor can be optimally designed with regard to strength andefficiency.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The axial flow machine according to the invention is described in moredetail below on the basis of an exemplary embodiment with reference tothe attached drawings, in which:

FIG. 1 shows an axial flow machine according to the invention in a sideview;

FIG. 2 shows the axial flow machine in a partial sectional view alongthe line II—II in FIG. 1;

FIG. 3 shows the rotor with machine shaft and with means for determiningthe magnetic pole position of the rotor in a side view;

FIG. 4 shows the rotor including the machine shaft in a partialsectional view along the line IV—IV in FIG. 3;

FIG. 5 shows an enlarged view of a detail of the rotor from FIG. 4;

FIG. 6 shows a plan view of a segmented permanent magnet;

FIG. 7 shows a sectional view of the segmented permanent magnet alongthe line VII—VII in FIG. 6;

FIG. 8 shows a permanent magnet with a first special contour for thepositive connection with the surrounding plastic;

FIG. 9 shows a permanent magnet with a second special contour for thepositive connection with the surrounding plastic;

FIG. 10 shows a stator in a side view; and

FIG. 11 shows a sectional view of the stator along the line XI—XI inFIG. 10.

DETAILED DESCRIPTION

FIGS. 1 and 2

The axial flow machine according to the invention which is showncomprises a disk-shaped rotor 1, which is securely connected to amachine shaft 2 and has permanent magnets 11, which are embedded in afiber-reinforced plastic 12, for example a thermosetting material.Arranged on both sides of the rotor 1 there is in each case, parallel tothe latter, an annular stator 3 and 4, which is respectively fastened toa bearing plate 6. The stators 3, 4 each have an annular yoke 31 and 41with slots 32 and 42 on their sides facing the rotor 1, in which slotsmulti-phase windings 33 and 43 which have external winding overhangs 331and 431 are led. The bearing plates 6 are preferably made of aluminumand also have stiffening and cooling ribs 63, with the result that theheat generated is dissipated well. Clearances 64 in the bearing plates 6have the purpose of reducing the weight. For mounting the bearing plates6, bolt holes 61 are provided, while threaded holes 62 serve forfastening them on a machine part, not shown, for example a gearmechanism. The bearing plates 6 and an annular casing part 8 togetherform a casing for the rotor 1 and the stators 3, 4. The machine shaft 2is rotatably mounted on the bearing plates 6 by means of ball bearings7.

The two stators 3, 4 are electrically offset in relation to one anotherin the circumferential direction by 180°, with the result that thecorresponding magnetic fluxes produced in the circumferential directionin the rotor 1 are oppositely oriented and consequently cancel oneanother out in practice, at least for the most part. This makes itpossible to dispense with an iron in the rotor 1.

The following statement applies to the entire further description. Ifreference numerals are contained in a figure for the purpose ofelucidating the drawing but are not mentioned in the directly associatedtext of the description, or vice versa, reference is made to theirexplanation in previous descriptions of figures.

FIGS. 3 to 5

According to the invention, the rotor 1 and the machine shaft 2 form adimensionally stable unit. The ironless disk-shaped rotor 1 has eightpermanent magnets 11, which are circumferentially arranged, in a circle,around the machine shaft 2 and are embedded in the fiber-reinforcedplastic 12. The fiber-reinforced plastic 12 extends between thepermanent magnets 11, altogether over between approximately 15% and 20%of the circle, to be precise, in uniform webs. In this way, there issufficient fiber-reinforced plastic 12 between the mechanically veryrigid permanent magnets 11 for the rotor 1 to be stable, and a rotor 1with the smallest possible mass moment of inertia is achieved with thegreatest economy, in terms of production cost.

The machine shaft 2 is also embedded in a central region in thefiber-reinforced plastic 12, two flanges 21 and 22 providing a stableconnection between the rotor 1 and the machine shaft 2.

For absorbing the centrifugal forces, attached to the outercircumference of the rotor 1 is a stiffening band 13, which comprisespreimpregnated fibrous material, which preferably contains glass, carbonor Kevlar fibers predominantly aligned in the circumferential direction.The stiffening band 13 is wider than the permanent magnets 11 and thefiber-reinforced plastic 12, which can be clearly seen in particular inFIG. 5. It is advantageous for stiffening purposes for thefiber-reinforced plastic 12 and the permanent magnets 11 also to beformed such that they become thicker from the inside outward.

Adhesively attached on the outside around the stiffening band 13 is amagnetic strip 14, which forms a radially magnetized series of magneticpoles, which are respectively arranged in a way corresponding to thepermanent magnets 11 embedded in the fiber-reinforced plastic 12,although 100% of the circumference is covered. This magnetic strip 14makes it possible to determine the magnetic pole position of the rotor 1at the periphery by means of three fixed-in-place Hall probes 5. Thethree Hall probes 5 are spaced apart from one another in thecircumferential direction by 30° each and are arranged for example on aprinted circuit, which is fastened to the casing part 8. The determinedmagnetic pole position allows the firing angle for the multi-phasewindings 33, 43 of the stators 3, 4 to be optimally set.

The permanent magnets 11 preferably consist of sintered magneticmaterial, for example NdFeB, with a flexural strength of approximately270 N/mm² and a modulus of elasticity of approximately 150 kN/mm². Thefiber-reinforced plastic 12 is, for example, an epoxy resin or an imideresin with glass fiber reinforcement. The mechanical strength valuesachieved here too lie in the range of steel 37. The heat resistance forthe epoxy resin lies around 200° C. and for the imide resin lies around250° C. For better thermal expansion and thermal conductivity, mineralsubstances may be additionally added to the resin.

To produce the rotor 1, the machine shaft 2 and the permanent magnets 11are arranged in a mold and the pre-heated fiber-reinforced plastic issubsequently poured under pressure into the mold, which is heated.Depending on the resin, the pouring-in of the fiber-reinforced plastictakes place at a temperature of at least 200° C. or at least 250° C. andunder a pressure of 500-1500 bar. This causes plastication, whichensures complete filling of the mold and a good positive fit with thepermanent magnets 11 and the machine shaft 2.

FIGS. 6 and 7

In the case of the present exemplary embodiment, the permanent magnets11 respectively comprise three separate magnet segments 111 next to oneanother in the circumferential direction. This allows the eddy currentlosses to be reduced. The magnet segments 111 are preferably joined bymeans of a metal adhesive, but may also be held together only by thefiber-reinforced plastic 12.

FIGS. 8 and 9

Since a great intrinsic rigidity of the rotor 1 is essential at highrotational speeds and with relatively small air gaps between the rotor 1and the stators 3, 4, the permanent magnets 11 are each joined with apositive, i.e., interference, fit to the surrounding fiber-reinforcedplastic 12. Shown in FIGS. 8 and 9 are two possible magnet contours,which are suitable for absorbing the shearing forces that occur in therotor. The generally planar magnets shown in plan and side views inFIGS. 6 and 7 are shown in partial side views in FIGS. 8 and 9. Thepermanent magnet 11 in FIG. 8 includes a projection in the form of aridge at the peripheral edge of the magnet. The projection is centrallylocated on the peripheral edge of the permanent magnet. The permanentmagnet 11 shown in side view in FIG. 9 includes a recess in theperipheral edge. That recess is in the form of a v-shaped groove that iscentrally located with respect to the peripheral edge of the permanentmagnet.

In the case of the rotor 1 shown, it is possible to dispense with theattachment on both sides of magnetically conductive plates for holdingthe permanent magnets 11 or a similar kind of sandwich design, wherebythe mass inertia, the amount of magnetic material and the surface lossescan be kept low and undesired leakage paths between neighboringpermanent magnets 11 can be avoided.

FIGS. 10 and 11

The construction of the two stators 3, 4 is explained below on the basisof the example of the stator 3. The stator 3 comprises an annular yoke31, in which slots 32 extending approximately radially from the insideoutward have been made. The yoke 31 is made up of a plurality of layers311 of high-quality dynamo sheet, which are rolled during the slotpunching to form assemblies and are subsequently connected by a weldpoint. The slots 32 are relatively wide in the interior of the yoke 32,but toward the rotor 1 have a relatively narrow opening 321.

As shown in FIG. 2, multi-phase windings 33, for example three-phasewindings, are led through the slots 32. Accommodating the multi-phasewindings 33 in the slots 32 allows the stator 3 to be brought close tothe permanent magnets 11 of the rotor 1, i.e. there is a very small airgap, which has the consequence of a very high magnetic flux andconsequently a very great power density.

On account of a transposing of the slots 32 in the circumferentialdirection and with respect to the permanent magnets 11 of the rotor 1,latching moments and noises can be minimized.

Further design variations can be realized in respect of the axial flowmachine described above. The following are also expressly mentionedhere:

The determination of the magnetic pole position of the rotor 1 does notnecessarily have to take place by means of the magnetic strip 14 and theHall probes 5. Also conceivable, inter alia, is an optical scanning oflight and dark regions on the periphery of the rotor 1.

Instead of transposing the slots 32, and consequently the multi-phasewindings 33 led in them, the permanent magnets 11 may also betransposed.

Instead of being fiber-reinforced, the plastic 12 of the rotor 1 mayalso be fabric-reinforced.

What is claimed is:
 1. An electric axial flow machine including anironless disk-shaped rotor arranged on a machine shaft and havingpermanent magnets embedded in a fiber- or fabric-reinforced plastic,and, on both sides, next to the rotor, a stator, wherein the permanentmagnets are each embedded in and joined at least peripherally in aninterference fit with the fiber- or fabric-reinforced plastic so thatthe permanent magnets and the machine shaft form a dimensionally stableunit.
 2. The electric axial flow machine as claimed in claim 1, whereinthe permanent magnets are arranged circumferentially, in a circle,around the machine shaft and the fiber- or fabric-reinforced plasticextends between the permanent magnets over at least 10% of the circle.3. The electric axial flow machine as claimed in claim 1, wherein therotor has on an outer circumference, or proximate the outercircumference, a stiffening band comprising preimpregnated fibrousmaterial, the rotor becoming thicker with increasing distance from themachine shaft.
 4. The electric axial flow machine as claimed in claim 1,comprising means for determining magnetic pole position of the rotorincluding a magnetic strip arranged on an outer circumference of therotor and having a radially magnetized series of magnetic poles arrangedin correspondence to the permanent magnets embedded in the fiber- orfabric-reinforced plastic, and fixed-in-place Hall probes interactingwith the magnetic poles.
 5. The electric axial flow machine as claimedin claim 1, wherein the fiber- or fabric-reinforced plastic comprises anepoxy resin or an imide resin with glass fiber reinforcement.
 6. Theelectric axial flow machine as claimed in claim 1, wherein the permanentmagnets respectively comprise at least two separate magnet segmentscontiguous to one another, in a circumferential direction, joined by ametal adhesive.
 7. The electric axial flow machine as claimed in claim1, wherein the stator comprises an annular yoke including slotsextending approximately radially, relative to the machine shaft, andthrough which multi-phase windings pass.
 8. The electric axial flowmachine as claimed in claim 7, wherein the permanent magnets areobliquely arranged, relive to radii of the machine shaft, along acircumferential direction.
 9. The electric axial flow machine as claimedin claim 1, including two stators electrically offset in relation to oneanother in a circumferential direction by 180° so that magnetic fluxesin the circumferential direction in the rotor are oppositely orientedand essentially cancel one another.
 10. A method for producing anironless disk-shaped rotor for arrangement on a machine shaft of anelectric axial flow machine and having permanent magnets embedded in afiber- or fabric-reinforced plastic, including placing the machine shaftand the permanent magnets in a mold, heating the mold, and injecting apre-heated fiber- or fabric-reinforced plastic under pressure into theheated mold to establish an interference fit between the permanentmagnets and the fiber- or fabric-reinforced plastic.
 11. The method asclaimed in claim 10, including injecting the fiber- or fabric-reinforcedplastic at a temperature of at least 200° C. and under a pressure of500-1500 bar.
 12. The electric axial flow machine as claimed in claim 7,wherein the slots are obliquely arranged, relative to radii of themachine shaft, along a circumferential direction.
 13. The electric axialflow machine as claimed in claim 1, wherein the permanent magnets aregenerally planar and include peripheral edges having recesses filledwith the fiber- or fabric-reinforced plastic, forming the interferencefit.
 14. The electric axial flow machine as claimed in claim 13, whereinthe recesses are grooves.
 15. The electric axial flow machine as claimedin claim 1, wherein the permanent magnets are generally planar andinclude peripheral edges having projections extending into the fiber- orfabric-reinforced plastic, forming the interference fit.
 16. Theelectric axial flow mache as claimed in claim 15, wherein theprojections are ridges.
 17. The method as claimed in claim 10, whereinthe permanent magnets are generally planar and include peripheral edgeshaving recesses, including injecting the pre-heated the fiber- orfabric-reinforced plastic into the recesses to form the interference fitbetween the permanent magnets and the fiber- or fabric-reinforcedplastic.
 18. The method as claimed in claim 17, wherein the recesses aregrooves.
 19. The method as claimed in claim 10, wherein the permanentmagnets are generally planar and include peripheral edges havingprojections and including injecting the pre-heated fiber- orfabric-reinforced plastic so that the projections form the interferencefit between the pennant magnets and the fiber- or fabric-reinforcedplastic.
 20. The method as claimed in claim 19, wherein the projectionsare ridges.